The present invention relates to an image forming apparatus operable with a two-side unit for selectively forming a plurality of images on one side of a paper sheet and forming images on opposite sides of a paper sheet.
Generally, an electrophotographic copier or similar image forming apparatus using an electrophotographic procedure is required to have not only an ordinary function of copying an image on one side of a paper sheet but also a a function of forming images on both sides of a paper sheet (hereinafter referred to as a two-side copying function) and a function of forming a plurality of images together on one side of a paper sheet (hereinafter referred to as a combined copying function). An image forming apparatus using a two-side unit which is suitable for implementing the two-side and combined copying functions has been proposed (e.g. Japanese Patent Laid-Open Publication No. 208470/1988). The two-side unit has a paper transport path and a switchback section thereinside and is operatively connected to the rear end of an apparatus from which a paper sheet will be driven out. A drawback with this kind of scheme is that an extra space for accommodating the two-side unit has to be provided at the rear of the apparatus body. Further, the two-side unit or a paper cassette is inserted into and drawn out from the apparatus body at the side where paper sheets are to be driven out. This degrades the operability in the event of replacement of the two-side unit or the paper cassette and results in the need for an additional space for accommodating the operator as well. Other drawbacks with such a prior art approach are that the two-side unit and paper cassette each needs a paper tray, and that the two-side unit and paper cassette are different in external configuration from each other and, therefore, troublesome to handle and transport.